It is well known to spray apply fireproofing slurries to metal structural members and other building surfaces in order to provide a heat resistant coating thereon. U.S. Pat. Nos. 3,719,513 and 3,839,059, which are incorporated herein by reference, disclosed gypsum-based formulations that contain, in addition to the gypsum binder, a lightweight inorganic aggregate such as vermiculite, a fibrous substance such as cellulose, and an air entraining agent.
U.S. Pat. No. 4,751,024, which is incorporated herein by reference, disclosed sprayable fireproofing compositions containing shredded polystyrene as a lightweight aggregate in fireproofing compositions.
Since fireproofing compositions are typically transported to the building site as dry mixtures, and are formed into slurries upon the addition of an appropriate amount of water, the preparation and application processes may span many hours. Thus, the setting time of the mix is generally heavily retarded to provide an acceptable field pot life. This retarding in the mixer contradicts the desired quick setting time upon spray application; it is highly desirable to achieve quick setting time in the composition upon spray-application to provide body to the fireproofing. Accordingly, a delicate balance between the use of retarding agents and accelerating agents is desirable and yet difficult to achieve. Obviously, if the mixture were to stiffen substantially in the hopper or mixer, it would be rendered non-pumpable and therefore would be useless for the intended application.
Such fireproofing slurries are generally prepared at ground level and pumped to the point of application, where they are spray-applied onto the substrate. Often, the point of application exceeds twenty or thirty stories where high rise construction is involved. U.S. Pat. Nos. 4,934,596 and 5,520,332, which are incorporated herein by reference, each disclose a method and apparatus which may be used for spray-application of fireproofing compositions through hoses and nozzles. An accelerator fluid is introduced by injection and distributed evenly within the flowing slurry to accelerate the setting of the spray-applied fireproofing composition upon application.
The inclusion of set retarding agents and set accelerating agents in sprayable fireproofing slurries is therefore not a matter of casual or intuitive selection. The formulation and preparation of such fireproofing slurries is complicated by the fact that pumpability is a critical characteristic: the formulated compositions must be able to hold the large quantity of water that renders them capable of being pumped easily and to great heights, yet they must retain a consistency sufficient to prevent segregation or settling of ingredients and permit adequate yield or coverage of the substrate at a given thickness. The compositions must be able to entrain air of a stable nature in order to be pumped through conventional fireproofing spray equipment. The coating mixes must adhere to the substrate both in the slurried state and in the dry state. Also, the mix must set without undue expansion or shrinkage which could result in the formation of cracks that would seriously deter from the insulative value of the dry coating.
Typically, the spray equipment, which includes the mixer, pump, hoses, nozzle, and other ancillary equipment, needs to be pumped clean with water at the end of an application job, to ensure that the sprayable composition does not have the opportunity to harden and plug up the equipment overnight. Thus, at the end of every work day, the applicators needed to take time to empty and clean their equipment. Moreover, the unused slurry, which is pumped out of the mixer and hoses, also becomes an environmental concern. Thus, current fireproofing formulations lead to the loss of production time and creation of waste. Current pumpable fireproofing slurries incorporate a protein-based material (e.g., horse hooves), in amounts of 0.2-0.25% based on weight of binder in the composition, which retards the setting of the slurry for approximately four to twelve hours.
Until the present invention, however, it has not been taught or suggested in the fireproofing industry to achieve a gypsum-based fireproofing composition for spray-application which is capable of delayed setting for at least 24 hours and up to 72-96 hours. The present inventors had privately surmised among themselves that protein-based set retarders could be used in an amount sufficient to delay the setting of the fireproofing composition overnight (e.g., sixteen to twenty-four hours) or over the weekend, and that the high level of proteinaceous set retarder would generate an extremely unpleasant odor. Moreover, where aesthetics are important, high amounts of such protein-containing set retarders may have detrimental effects in terms of staining the fireproofing coating that is applied and allowed to set in place.
However, it was not until internal testing was completed--as set forth hereinafter--that the inventors realized how inventive their earlier private surmisings about using delayed-set retarding agents, without destroying the fireproofing abilities of the gypsum-based fireproofing composition, was.